Fuel oxygen reduction unit for prescribed operating conditions

ABSTRACT

A fuel oxygen reduction unit for an engine is provided. The fuel oxygen reduction unit includes an inlet fuel line; a stripping gas source; a contactor selectively in fluid communication with the stripping gas source, the inlet fuel line, or both to form a fuel/gas mixture; and a separator that receives the fuel/gas mixture, the separator configured to separate the fuel/gas mixture into an outlet stripping gas flow and an outlet fuel flow; wherein a flow of stripping gas passes through the fuel oxygen reduction unit a single time.

FIELD OF THE INVENTION

The present subject matter relates generally to a fuel oxygen reductionunit for an engine and a method of operating the same.

BACKGROUND OF THE INVENTION

Typical aircraft propulsion systems include one or more gas turbineengines. The gas turbine engines generally include a turbomachine, theturbomachine including, in serial flow order, a compressor section, acombustion section, a turbine section, and an exhaust section. Inoperation, air is provided to an inlet of the compressor section whereone or more axial compressors progressively compress the air until itreaches the combustion section. Fuel is mixed with the compressed airand burned within the combustion section to provide combustion gases.The combustion gases are routed from the combustion section to theturbine section. The flow of combustion gasses through the turbinesection drives the turbine section and is then routed through theexhaust section, e.g., to atmosphere.

Certain operations and systems of the gas turbine engines and aircraftmay generate a relatively large amount of heat. Fuel has been determinedto be an efficient heat sink to receive at least some of such heatduring operations due at least in part to its heat capacity and anincreased efficiency in combustion operations that may result fromcombusting higher temperature fuel.

However, heating the fuel up without properly conditioning the fuel maycause the fuel to “coke,” or form solid particles that may clog upcertain components of the fuel system, such as the fuel nozzles.Reducing an amount of oxygen in the fuel may effectively reduce thelikelihood that the fuel will coke beyond an unacceptable amount.

BRIEF DESCRIPTION OF THE INVENTION

Aspects and advantages of the invention will be set forth in part in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

In one exemplary embodiment of the present disclosure, a fuel oxygenreduction unit for an engine is provided. The fuel oxygen reduction unitincludes an inlet fuel line; a stripping gas source; a contactorselectively in fluid communication with the stripping gas source, theinlet fuel line, or both to form a fuel/gas mixture; and a separatorthat receives the fuel/gas mixture, the separator configured to separatethe fuel/gas mixture into an outlet stripping gas flow and an outletfuel flow; wherein a flow of stripping gas passes through the fueloxygen reduction unit a single time.

In certain exemplary embodiments the fuel oxygen reduction unit includesa valve downstream of the stripping gas source and upstream of thecontactor, wherein the valve is transitionable between a closed positionin which the stripping gas source is not in fluid communication with thecontactor, and an open position in which the stripping gas flows to thecontactor.

In certain exemplary embodiments the valve transitions to the openposition at a prescribed operating condition.

In certain exemplary embodiments the prescribed operating condition is aweight on wheels condition.

In certain exemplary embodiments the prescribed operating condition isan engine speed condition.

In certain exemplary embodiments the prescribed operating condition is awind down condition of the engine.

In certain exemplary embodiments the fuel oxygen reduction unit definesa maximum continuous operating time of one hour or less.

In certain exemplary embodiments the separator includes an inlet influid communication with the contactor that receives the fuel/gasmixture, a fuel outlet, and a stripping gas outlet, wherein theseparator is configured to separate the fuel/gas mixture into an outletstripping gas flow and an outlet fuel flow and provide the outletstripping gas flow to the stripping gas outlet and the outlet fuel flowto the fuel outlet.

In certain exemplary embodiments the outlet stripping gas flow is ventedout to atmosphere downstream of the separator.

In certain exemplary embodiments the stripping gas source comprises arechargeable bottle of inert gas.

In certain exemplary embodiments the stripping gas source comprises aninert gas generator.

In certain exemplary embodiments the outlet fuel flow has a lower oxygencontent than the inlet fuel flow, and wherein the outlet stripping gasflow has a higher oxygen content than the inlet stripping gas flow.

In another exemplary embodiment of the present disclosure, a fuel oxygenreduction system for an engine is provided. The fuel oxygen reductionsystem includes an inlet fuel line; a stripping gas source; a contactorselectively in fluid communication with the stripping gas source, theinlet fuel line, or both to form a fuel/gas mixture; a separator thatreceives the fuel/gas mixture, the separator configured to separate thefuel/gas mixture into an outlet stripping gas flow and an outlet fuelflow; and a storage tank that receives the outlet fuel flow.

In certain exemplary embodiments the stripping gas source comprises aninert gas generator.

In certain exemplary embodiments the fuel oxygen reduction systemincludes a primary tank containing a primary fuel flow; and a valvedownstream of the storage tank and the primary tank, wherein the valveis transitionable between a first position in which the primary tank isin fluid communication with the engine, and a second position in whichthe storage tank is in fluid communication with the engine.

In certain exemplary embodiments the valve transitions to the secondposition at a prescribed operating condition.

In certain exemplary embodiments the prescribed operating condition is aweight on wheels condition.

In certain exemplary embodiments the prescribed operating condition isan engine speed condition.

In certain exemplary embodiments the primary tank defines a firstvolume, wherein the storage tank defines a second volume, and whereinthe second volume is less than 20% of the first volume.

In certain exemplary embodiments the separator includes an inlet influid communication with the contactor that receives the fuel/gasmixture, a fuel outlet, and a stripping gas outlet, wherein theseparator is configured to provide the outlet stripping gas flow to thestripping gas outlet and the outlet fuel flow to the storage tank viathe fuel outlet.

In an exemplary aspect of the present disclosure, a method is providedfor operating a fuel delivery system for a gas turbine engine. Themethod includes receiving an inlet fuel flow in a fuel oxygen reductionunit for reducing an amount of oxygen in the inlet fuel flow using astripping gas flow through a stripping gas flowpath; and passing thestripping gas flow through the fuel oxygen reduction unit a single time.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims. The accompanying drawings, which areincorporated in and constitute a part of this specification, illustrateembodiments of the invention and, together with the description, serveto explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth in the specification, which makes reference to the appendedfigures, in which:

FIG. 1 is a schematic, cross-sectional view of a gas turbine engine inaccordance with an exemplary embodiment of the present disclosure.

FIG. 2 is a schematic view of a fuel oxygen reduction unit in accordancewith an exemplary embodiment of the present disclosure.

FIG. 3A is a schematic view of a fuel oxygen reduction unit inaccordance with another exemplary embodiment of the present disclosure.

FIG. 3B is a schematic view of an inert gas generator in accordance withan exemplary embodiment of the present disclosure.

FIG. 3C is a schematic view of an inert gas generator in accordance withanother exemplary embodiment of the present disclosure.

FIG. 4 is a schematic view of a fuel oxygen reduction system inaccordance with an exemplary embodiment of the present disclosure.

FIG. 5 is a schematic view of a fuel oxygen reduction system inaccordance with another exemplary embodiment of the present disclosure.

FIG. 6 is a flow diagram of a method of operating a fuel system for anaeronautical gas turbine engine in accordance with an aspect of thepresent disclosure.

FIG. 7 is a flow diagram of a method of operating a fuel system for anaeronautical gas turbine engine in accordance with another aspect of thepresent disclosure.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereinillustrate exemplary embodiments of the disclosure, and suchexemplifications are not to be construed as limiting the scope of thedisclosure in any manner.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to present embodiments of theinvention, one or more examples of which are illustrated in theaccompanying drawings. The detailed description uses numerical andletter designations to refer to features in the drawings. Like orsimilar designations in the drawings and description have been used torefer to like or similar parts of the invention.

The following description is provided to enable those skilled in the artto make and use the described embodiments contemplated for carrying outthe invention. Various modifications, equivalents, variations, andalternatives, however, will remain readily apparent to those skilled inthe art. Any and all such modifications, variations, equivalents, andalternatives are intended to fall within the spirit and scope of thepresent invention.

For purposes of the description hereinafter, the terms “upper”, “lower”,“right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, “lateral”,“longitudinal”, and derivatives thereof shall relate to the invention asit is oriented in the drawing figures. However, it is to be understoodthat the invention may assume various alternative variations, exceptwhere expressly specified to the contrary. It is also to be understoodthat the specific devices illustrated in the attached drawings, anddescribed in the following specification, are simply exemplaryembodiments of the invention. Hence, specific dimensions and otherphysical characteristics related to the embodiments disclosed herein arenot to be considered as limiting.

As used herein, the terms “first”, “second”, and “third” may be usedinterchangeably to distinguish one component from another and are notintended to signify location or importance of the individual components.

The terms “upstream” and “downstream” refer to the relative directionwith respect to fluid flow in a fluid pathway. For example, “upstream”refers to the direction from which the fluid flows, and “downstream”refers to the direction to which the fluid flows.

The terms “coupled,” “fixed,” “attached to,” and the like refer to bothdirect coupling, fixing, or attaching, as well as indirect coupling,fixing, or attaching through one or more intermediate components orfeatures, unless otherwise specified herein.

The singular forms “a”, “an”, and “the” include plural references unlessthe context clearly dictates otherwise.

Approximating language, as used herein throughout the specification andclaims, is applied to modify any quantitative representation that couldpermissibly vary without resulting in a change in the basic function towhich it is related. Accordingly, a value modified by a term or terms,such as “about”, “approximately”, and “substantially”, are not to belimited to the precise value specified. In at least some instances, theapproximating language may correspond to the precision of an instrumentfor measuring the value, or the precision of the methods or machines forconstructing or manufacturing the components and/or systems. Forexample, the approximating language may refer to being within a 10percent margin.

Here and throughout the specification and claims, range limitations arecombined and interchanged, such ranges are identified and include allthe sub-ranges contained therein unless context or language indicatesotherwise. For example, all ranges disclosed herein are inclusive of theendpoints, and the endpoints are independently combinable with eachother.

In a fuel oxygen reduction unit of the present disclosure, the fueloxygen reduction unit is a static system that is configured and sizedfor operating, e.g., deoxygenating fuel, at a prescribed operatingcondition. Additionally, the fuel oxygen reduction unit of the presentdisclose can be retrofitted on existing engine systems and/orincorporated into a new engine system.

In a fuel oxygen reduction system of the present disclosure, the fueloxygen reduction system provides a system that continuously deoxygenatesfuel and then stores the deoxygenated fuel in a storage tank. Thisdeoxygenated fuel stored in the storage tank is then provided to anengine at a prescribed operating condition.

Referring now to the drawings, wherein identical numerals indicate thesame elements throughout the figures, FIG. 1 provides a schematic,cross-sectional view of an engine in accordance with an exemplaryembodiment of the present disclosure. The engine may be incorporatedinto a vehicle. For example, the engine may be an aeronautical engineincorporated into an aircraft. Alternatively, however, the engine may beany other suitable type of engine for any other suitable aircraft.

For the embodiment depicted, the engine is configured as a high bypassturbofan engine 100. As shown in FIG. 1 , the turbofan engine 100defines an axial direction A (extending parallel to a longitudinalcenterline or axis 101 provided for reference), a radial direction R,and a circumferential direction (extending about the axial direction A;not depicted in FIG. 1 ). In general, the turbofan 100 includes a fansection 102 and a turbomachine 104 disposed downstream from the fansection 102.

The exemplary turbomachine 104 depicted generally includes asubstantially tubular outer casing 106 that defines an annular inlet108. The outer casing 106 encases, in serial flow relationship, acompressor section including a booster or low pressure (LP) compressor110 and a high pressure (HP) compressor 112; a combustion section 114; aturbine section including a high pressure (HP) turbine 116 and a lowpressure (LP) turbine 118; and a jet exhaust nozzle section 120. Thecompressor section, combustion section 114, and turbine section togetherdefine at least in part a core air flowpath 121 extending from theannular inlet 108 to the jet nozzle exhaust section 120. The turbofanengine further includes one or more drive shafts. More specifically, theturbofan engine includes a high pressure (HP) shaft or spool 122drivingly connecting the HP turbine 116 to the HP compressor 112, and alow pressure (LP) shaft or spool 124 drivingly connecting the LP turbine118 to the LP compressor 110.

For the embodiment depicted, the fan section 102 includes a fan 126having a plurality of fan blades 128 coupled to a disk 130 in a spacedapart manner. The fan blades 128 and disk 130 are together rotatableabout the longitudinal axis 101 by the LP shaft 124. The disk 130 iscovered by rotatable front hub 132 aerodynamically contoured to promotean airflow through the plurality of fan blades 128. Further, an annularfan casing or outer nacelle 134 is provided, circumferentiallysurrounding the fan 126 and/or at least a portion of the turbomachine104. The nacelle 134 is supported relative to the turbomachine 104 by aplurality of circumferentially-spaced outlet guide vanes 136. Adownstream section 138 of the nacelle 134 extends over an outer portionof the turbomachine 104 so as to define a bypass airflow passage 140therebetween.

Referring still to FIG. 1 , the turbofan engine 100 additionallyincludes an accessory gearbox 142, a fuel oxygen reduction unit orsystem 144, and a fuel delivery system 146. For the embodiment shown,the accessory gearbox 142 is located within the cowling/outer casing 106of the turbomachine 104. Additionally, it will be appreciated that,although not depicted schematically in FIG. 1 , the accessory gearbox142 may be mechanically coupled to, and rotatable with, one or moreshafts or spools of the turbomachine 104. For example, in at leastcertain exemplary embodiments, the accessory gearbox 142 may bemechanically coupled to, and rotatable with, the HP shaft 122. Further,for the embodiment shown, the fuel oxygen reduction unit 144 may becoupled to, or otherwise rotatable with, the accessory gearbox 142. Insuch a manner, it will be appreciated that the exemplary fuel oxygenreduction unit 144 may be driven by the accessory gearbox 142. In otherexemplary embodiments, the exemplary fuel oxygen reduction unit 144 maybe driven by other sources. Notably, as used herein, the term “fueloxygen conversion” generally means a device capable of reducing a freeoxygen content of the fuel.

Moreover, the fuel delivery system 146 generally includes a fuel source148, such as a fuel tank, and one or more fuel lines 150. The one ormore fuel lines 150 provide a fuel flow through the fuel delivery system146 to the combustion section 114 of the turbomachine 104 of theturbofan engine 100. In exemplary engine configurations, the combustionsection 114 includes a plurality of fuel nozzles circumferentially aboutthe centerline axis 101. These fuel nozzles define a plurality of fuelflow passages that define a volume, such that when fuel flow to thenozzle ceases, a volume of fuel remains within the nozzle.

During typical operations in such configurations, the primary fueloxygen reduction unit 144 may operate to reduce an oxygen content of afuel flow to the combustion section 114, and more particularly to suchfuel nozzles. During a wind down condition, however, it may be necessaryto further reduce an oxygen content of the fuel. For example, dependingon, e.g., a thermal mass of a core of the engine 100 and a turbine inlettemperature during an idle condition of the engine, heat from the coreof the engine 100 may “soak-back” to these fuel nozzles, heating thevolume of fuel remaining within the fuel nozzles to a point that thevolume of fuel remaining within the fuel nozzles would coke unless anoxygen content of such volume of fuel is reduced below the levelsprovided by an exemplary fuel oxygen reduction unit 144 of the presentdisclosure.

Accordingly, an exemplary fuel oxygen reduction unit 144 of the presentdisclosure may be operated during the wind down condition to ensure thatthe volume of fuel remaining within the fuel nozzle after the engine hasshut down is sufficiently low to prevent the fuel flow coking orotherwise deteriorating past an undesired level when the heat from thecore of the engine 100 soaks-back to such fuel nozzles.

It will be appreciated, however, that the exemplary turbofan engine 100depicted in FIG. 1 is provided by way of example only. In otherexemplary embodiments, any other suitable engine may be utilized withaspects of the present disclosure. For example, in other embodiments,the engine may be any other suitable gas turbine engine, such as aturboshaft engine, turboprop engine, turbojet engine, etc. In such amanner, it will further be appreciated that in other embodiments the gasturbine engine may have any other suitable configuration, such as anyother suitable number or arrangement of shafts, compressors, turbines,fans, etc. Further, although the exemplary gas turbine engine depictedin FIG. 1 is shown schematically as a direct drive, fixed-pitch turbofanengine 100, in other embodiments, a gas turbine engine of the presentdisclosure may be a geared gas turbine engine (i.e., including a gearboxbetween the fan 126 and shaft driving the fan, such as the LP shaft124), may be a variable pitch gas turbine engine (i.e., including a fan126 having a plurality of fan blades 128 rotatable about theirrespective pitch axes), etc. Further, although not depicted herein, inother embodiments the gas turbine engine may be any other suitable typeof gas turbine engine, such as an industrial gas turbine engineincorporated into a power generation system, a nautical gas turbineengine, etc. Further, still, in alternative embodiments, aspects of thepresent disclosure may be incorporated into, or otherwise utilized with,any other type of engine, such as reciprocating engines.

Moreover, it will be appreciated that although for the embodimentdepicted, the turbofan engine 100 includes the fuel oxygen reductionunit 144 positioned within the turbomachine 104, i.e., within the casing106 of the turbomachine 104, in other embodiments, the fuel oxygenreduction unit 144 may be positioned at any other suitable location. Forexample, in other embodiments, the fuel oxygen reduction unit 144 mayinstead be positioned remote from the turbofan engine 100, such asproximate to, or within, the tank of the fuel delivery system 146.Additionally, in other embodiments, the fuel oxygen reduction unit 144may additionally or alternatively be driven by other suitable powersources such as an electric motor, a hydraulic motor, or an independentmechanical coupling to the HP or LP shaft, etc.

Referring now to FIG. 2 , a schematic drawing of a fuel oxygen reductionunit 200 for a gas turbine engine in accordance with an exemplaryembodiment of the present disclosure is provided. In at least certainexemplary embodiments, the exemplary fuel oxygen reduction unit 200depicted may be incorporated into, e.g., the exemplary engine 100described above with reference to FIG. 1 (e.g., may be the fuel oxygenreduction unit 144 depicted in FIG. 1 and described above). Fuel oxygenreduction unit 200 of the present disclose may be a static system thatis configured and sized for operating at a prescribed operatingcondition. Additionally, fuel oxygen reduction unit 200 of the presentdisclose can be retrofitted on existing engine systems and/orincorporated into a new engine system.

As will be appreciated from the discussion herein, in an exemplaryembodiment, the exemplary fuel oxygen reduction unit 200 of FIG. 2generally includes a contactor 202, a separator 204, a stripping gassource 210, and a valve 212. In an exemplary embodiment, the exemplaryfuel oxygen reduction unit 200 generally defines a single pass gasflowpath or single pass system 206 from the stripping gas source 210 tothe contactor 202 and out the separator 204 as described herein. Inparticular, for the embodiment shown, the fuel oxygen reduction unit 200is configured to pass a flow of stripping gas through the fuel oxygenreduction unit 200 a single time. For example, the flow of stripping gaspasses through the fuel oxygen reduction unit 200 a single time and thenmay be exited from the system to atmosphere.

In such a manner, it will be appreciated that the term “a single time”as used with respect to the passing of a stripping gas flow through thefuel oxygen reduction unit refers to the stripping gas flow not beingrecirculated in a continuous manner throughout all flightperiods/operation modes of an engine and/or aircraft incorporating thefuel oxygen reduction unit 200. In such a manner, it will be appreciatedthat the term “a single time” as used with respect to the passing of astripping gas flow through the fuel oxygen reduction unit may refer tothe stripping as not being recirculated through the fuel oxygenreduction unit 200 during operation (i.e., not providing an outletstripping gas flow 229 back as an inlet flow of stripping gas 220 to thecontactor 202). It will also be appreciated that the term “a singletime” as used with respect to the passing of a stripping gas flowthrough the fuel oxygen reduction unit refers to passing a stripping gasflow through a fuel oxygen reduction unit devoid of gas oxygen reductionfeatures, such as catalysts, pre-heaters, membranes, or similarfeatures. Additionally or alternatively, it will be appreciated that theterm “a single time” as used with respect to the passing of a strippinggas flow through the fuel oxygen reduction unit may refer to aparticular volume of stripping gas only being used one particular flightperiod or flight mission of an aircraft incorporating the fuel oxygenreduction unit. For example, the flight period or flight mission may bea wind down condition of the engine operable with/incorporating the fueloxygen reduction unit. Such may ensure a relatively low oxygen contentfuel is left in the engine at shutdown, such that a risk of damage tocertain components of the engine (such as the fuel nozzles) is minimizedas a result of heat soak-back at shutdown. Additionally oralternatively, still, it will be appreciated that the term “a singletime” as used with respect to the passing of a stripping gas flowthrough the fuel oxygen reduction unit may refer to a particular volumeof the stripping gas flow only being used for a single time period, suchas one (1) hour or less, or thirty (30) minutes or less. Accordingly, itwill be appreciated that in at least one exemplary embodiment, the fueloxygen reduction unit 200 defines a maximum continuous operating time ofone hour or less.

In exemplary embodiments, the contactor 202 may be configured in anysuitable manner to substantially mix a received gas and liquid flow. Forexample, the contactor 202 may, in certain embodiments, be amechanically driven contactor (e.g., having paddles for mixing thereceived flows), or alternatively may be a passive contactor for mixingthe received flows using, at least in part, a pressure and/or flowrateof the received flows. For example, a passive contactor may include oneor more turbulators, a venturi mixer, etc.

It will be appreciated that the fuel oxygen reduction unit 200 generallyprovides for a flow of stripping gas 220 to the contactor 202 for mixingwith a fuel flow during operation. It will be appreciated that the term“stripping gas” is used herein as a term of convenience to refer to agas generally capable of performing the functions described herein. Thestripping gas 220 may be an actual stripping gas functioning to stripoxygen from the fuel within the contactor, or alternatively may be asparging gas bubbled through a liquid fuel to reduce an oxygen contentof such fuel. For example, as will be discussed in greater detail below,the stripping gas 220 may be an inert gas, such as Nitrogen or CarbonDioxide (CO2), a gas mixture made up of at least 50% by mass inert gas,or some other gas or gas mixture having a relatively low oxygen content.

Referring to FIG. 2 , in an exemplary embodiment, the separator 204generally includes a stripping gas outlet 214, a fuel outlet 216, and aninlet 218. It will also be appreciated that the exemplary fuel oxygenreduction unit 200 depicted is operable with a fuel delivery system 146,such as a fuel delivery system 146 of the gas turbine engine includingthe fuel oxygen reduction unit 200 (see, e.g., FIG. 1 ). The exemplaryfuel delivery system 146 generally includes a plurality of fuel lines,and in particular, an inlet fuel line 222 and an outlet fuel line 224.The inlet fuel line 222 is fluidly connected to the contactor 202 forproviding a flow of liquid fuel or inlet fuel flow 226 to the contactor202 (e.g., from a fuel source, such as a fuel tank) and the outlet fuelline 224 is fluidly connected to the fuel outlet 216 of the separator204 for receiving a flow of deoxygenated liquid fuel or outlet fuel flow227.

Moreover, during typical operations, a flow of stripping gas 220 flowsto the contactor 202, wherein the stripping gas 220 is mixed with theflow of inlet fuel 226 from the inlet fuel line 222 to generate a fuelgas mixture 228. The fuel gas mixture 228 generated within the contactor202 is provided to the inlet 218 of the separator 204. The stripping gassource 210 is selectively in fluid communication with a stripping gasinlet of the contactor 202 for selectively introducing a stripping gasto the contactor 202.

For the embodiment depicted, the stripping gas source 210 is in fluidcommunication with the contactor 202 via the valve 212, which may beactuatable to supply the stripping gas flow 220 to the contactor 202 ata prescribed operating condition. Referring to FIG. 2 , the valve 212 isdownstream of the stripping gas source 210 and upstream of the contactor202. The valve 212 is transitionable between a closed position in whichthe stripping gas source 210 is not in fluid communication with thecontactor 202, and an open position in which the stripping gas 220 flowsto the contactor 220. As described herein, the valve 212 transitions tothe open position at a prescribed operating condition. In this manner,the fuel oxygen reduction unit 200 of the present disclosure operatesonly during desired engine parameters, e.g., parameters indicating theengine is at the end of the cycle. This enables the fuel oxygenreduction unit 200 of the present disclosure to be a static, smaller,and lighter unit to deoxygenate the fuel at the end of an engine cycle,for example, to prevent coking of the fuel. In other words, the fueloxygen reduction unit 200 of the present disclosure lowers the oxygencontent of the fuel, such that a relatively high amount of heat may beadded thereto with a reduced risk of the fuel coking (i.e., chemicallyreacting to form solid particles which may clog up or otherwise damagecomponents within the fuel flow path).

The prescribed operating condition can be any desired engine parameter.For example, the prescribed operating condition may be a weight onwheels condition indicating the end of an engine cycle. Also, theprescribed operating condition may be an engine speed condition, a winddown condition of the engine, time condition, or other engine parametercondition.

Generally, it will be appreciated that during operation of the fueloxygen reduction unit 200, the inlet fuel 226 provided through the inletfuel line 222 to the contactor 202 may have a relatively high oxygencontent. The stripping gas 220 provided to the contactor 202 may have arelatively low oxygen content or other specific chemical structure.Within the contactor 202, the inlet fuel 226 is mixed with the strippinggas 220, resulting in the fuel gas mixture 228. As a result of suchmixing a physical exchange may occur whereby at least a portion of theoxygen within the inlet fuel 226 is transferred to the stripping gas220, such that the fuel component of the mixture 228 has a relativelylow oxygen content (as compared to the inlet fuel 226 provided throughinlet fuel line 222) and the stripping gas component of the mixture 228has a relatively high oxygen content (as compared to the inlet strippinggas 220 provided to the contactor 202).

Within the separator 204 the relatively high oxygen content strippinggas 220 is then separated from the relatively low oxygen content fuel226 back into respective flows of an outlet stripping gas 229 and outletfuel 227. The separator 204 is configured to separate the fuel/gasmixture 228 into an outlet stripping gas flow 229 and an outlet fuelflow 227 and provide the outlet stripping gas flow 229 to the strippinggas outlet 214 and the outlet fuel flow 227 to the fuel outlet 216. Inan exemplary embodiment, the outlet stripping gas flow 229 is vented outto atmosphere downstream of the separator 204.

Further, it will be appreciated that the outlet fuel 227 provided to thefuel outlet 216, having interacted with the stripping gas 220, may havea relatively low oxygen content, such that a relatively high amount ofheat may be added thereto with a reduced risk of the fuel coking (i.e.,chemically reacting to form solid particles which may clog up orotherwise damage components within the fuel flow path). For example, inat least certain exemplary aspects, the outlet fuel 227 provided to thefuel outlet 216 may have an oxygen content of less than about five (5)parts per million (“ppm”), such as less than about three (3) ppm, suchas less than about two (2) ppm, such as less than about one (1) ppm,such as less than about 0.5 ppm.

Referring to FIG. 2 , in an exemplary embodiment, the stripping gassource 210 is a rechargeable bottle of inert gas 232. The bottle ofinert gas 232 could be positioned somewhere on the engine 100 oraircraft. The bottle 232 stores an amount of inert gas that is oxygenfree, e.g., a CO2 or N2 gas. The bottle 232 can be recharged at standardintervals.

Referring to FIG. 3A, in an exemplary embodiment, the stripping gassource 210 is an inert gas generator 234. The inert gas generator 234 isable to take air from some source, e.g., air from atmosphere, air from apump, air from the compressor bleed, and generate a continuous supply ofinert gas. In an exemplary embodiment, the inert gas generator 234 isused to continuously replenish a supply of inert gas to the bottle ofinert gas 232 described above.

For example, referring to FIG. 3B, in a first exemplary embodiment, theinert gas generator 234 is a membrane 236. The membrane 236 separatesoxygen out from nitrogen, for example. In this manner, an oxygen freestripping gas is continuously provided to the system.

Referring to FIG. 3C, in a second exemplary embodiment, the inert gasgenerator 234 is a pressure swing adsorption (PSA) system 238. The PSAsystem 238 is used to separate a first gas species from a mixture ofgases under pressure according to the species' molecular characteristicsand affinity for an adsorbent material. The PSA system 238 of thepresent disclosure separates a gas such as nitrogen, for example, fromoxygen. In this manner, an oxygen free stripping gas is continuouslyprovided to the system.

Referring now to FIG. 4 , a schematic drawing of a fuel oxygen reductionsystem 400 for a gas turbine engine in accordance with an exemplaryembodiment of the present disclosure is provided. In at least certainexemplary embodiments, the exemplary fuel oxygen reduction system 400depicted may be incorporated into, e.g., the exemplary engine 100described above with reference to FIG. 1 (e.g., may be the fuel oxygenreduction unit 144 depicted in FIG. 1 and described above). Fuel oxygenreduction system 400 of the present disclose may be a static system thatis configured and sized for operating at a prescribed operatingcondition.

The embodiment illustrated in FIG. 4 includes similar components to theembodiments illustrated in FIGS. 2-3A. For the sake of brevity, thesesimilar components will not all be discussed in conjunction with theembodiment illustrated in FIG. 4 .

As will be appreciated from the discussion herein, in an exemplaryembodiment, the exemplary fuel oxygen reduction system 400 of FIG. 4generally includes a contactor 402, a separator 404, a stripping gassource 410, a storage tank 411, a first valve 412, a primary tank 413,and a second valve 415. In an exemplary embodiment, the exemplary fueloxygen reduction system 400 generally defines a single pass gas flowpathor system 406 from the stripping gas source 410 to the contactor 402 andout the separator 404 as described herein. In an exemplary embodiment ofthe present disclosure, the primary tank 413 defines a first volume, thestorage tank 411 defines a second volume, and the second volume is lessthan 20% of the first volume. However, it is contemplated that thesecond volume may have other sizes relative to the first volume.

In exemplary embodiments, the contactor 402 may be configured in anysuitable manner to substantially mix a received gas and liquid flow. Forexample, the contactor 402 may, in certain embodiments, be amechanically driven contactor (e.g., having paddles for mixing thereceived flows), or alternatively may be a passive contactor for mixingthe received flows using, at least in part, a pressure and/or flowrateof the received flows. For example, a passive contactor may include oneor more turbulators, a venturi mixer, etc.

Fuel oxygen reduction system 400 of the present disclosure provides asystem that continuously deoxygenates fuel and then stores thedeoxygenated fuel in the storage tank 411. This deoxygenated fuel storedin storage tank 411 can then be provided to the engine at a prescribedoperating condition.

It will be appreciated that the fuel oxygen reduction system 400generally provides for a flow of stripping gas 420 to the contactor 402for mixing with a fuel flow during operation to continuously providedeoxygenated fuel that can be stored in storage tank 411.

Referring to FIG. 4 , in an exemplary embodiment, the stripping gassource 410 is an inert gas generator 434. As described above, the inertgas generator 434 is able to take air from some source, e.g., air fromatmosphere, air from a pump, air from the compressor bleed, and generatea continuous supply of inert gas.

During typical operations, a flow of stripping gas 420 flows to thecontactor 402, wherein the stripping gas 420 is mixed with the flow ofinlet fuel 426 from the inlet fuel line 422 to generate a fuel gasmixture 428. The fuel gas mixture 428 generated within the contactor 402is provided to the inlet 418 of the separator 404. The stripping gassource 410 is selectively in fluid communication with a stripping gasinlet of the contactor 402 for selectively introducing a stripping gasto the contactor 402.

As described above, the stripping gas source 410 is in fluidcommunication with the contactor 402 via a first valve 412, which may beactuatable to supply the stripping gas flow 420 to the contactor 402.Referring to FIG. 4 , the first valve 412 is downstream of the strippinggas source 410 and upstream of the contactor 402. The first valve 412 istransitionable between a closed position in which the stripping gassource 410 is not in fluid communication with the contactor 402, and anopen position in which the stripping gas 420 flows to the contactor 420.

Generally, it will be appreciated that during operation of the fueloxygen reduction system 400, the inlet fuel 426 provided through theinlet fuel line 422 to the contactor 402 may have a relatively highoxygen content. The stripping gas 420 provided to the contactor 402 mayhave a relatively low oxygen content or other specific chemicalstructure. Within the contactor 402, the inlet fuel 426 is mixed withthe stripping gas 420, resulting in the fuel gas mixture 428. As aresult of such mixing a physical exchange may occur whereby at least aportion of the oxygen within the inlet fuel 426 is transferred to thestripping gas 420, such that the fuel component of the mixture 428 has arelatively low oxygen content (as compared to the inlet fuel 426provided through inlet fuel line 422) and the stripping gas component ofthe mixture 428 has a relatively high oxygen content (as compared to theinlet stripping gas 420 provided to the contactor 402).

Within the separator 404 the relatively high oxygen content strippinggas 420 is then separated from the relatively low oxygen content fuel426 back into respective flows of an outlet stripping gas 429 and outletfuel 427. The separator 404 is configured to separate the fuel/gasmixture 428 into an outlet stripping gas flow 429 and an outlet fuelflow 427 and provide the outlet stripping gas flow 429 to the strippinggas outlet 414 and the outlet fuel flow 427 to the fuel outlet 416. Inan exemplary embodiment, the outlet stripping gas flow 429 is vented outto atmosphere downstream of the separator 404.

Further, it will be appreciated that the outlet fuel 427 provided to thefuel outlet 416, having interacted with the stripping gas 420, may havea relatively low oxygen content, such that a relatively high amount ofheat may be added thereto with a reduced risk of the fuel coking (i.e.,chemically reacting to form solid particles which may clog up orotherwise damage components within the fuel flow path).

This deoxygenated fuel 427 is then provided and stored in storage tank411 and can be provided to the engine at a prescribed operatingcondition.

Referring to FIG. 4 , in an exemplary embodiment, the fuel oxygenreduction system 400 includes a primary tank 413 containing a primaryfuel flow 440 and a second valve 415 that is downstream of the storagetank 411 and that is downstream of the primary tank 413. The primaryfuel flow 440 has a higher oxygen content than the deoxygenated fuel427.

The second valve 415 is transitionable between a first position in whichthe primary tank 413 is in fluid communication with the engine 100, anda second position in which the storage tank 411 is in fluidcommunication with the engine 100. With the second valve 415 in thefirst position, the primary fuel flow 440 from the primary tank 413 isprovided to the engine 100. With the second valve 415 in the secondposition, the deoxygenated fuel 427 from the storage tank 411 isprovided to the engine 100. In this manner, the fuel oxygen reductionsystem 400 of the present disclosure allows a switch that can transitionfrom providing a primary fuel flow 440 to the engine 100 or adeoxygenated fuel 427 to the engine 100.

The fuel oxygen reduction system 400 includes a second valve 415 thattransitions to the second position at a prescribed operating condition.In this manner, the deoxygenated fuel 427 from the storage tank 411 isprovided to the engine 100 only during desired engine parameters, e.g.,parameters indicating the engine 100 is at the end of the cycle. Theprescribed operating condition can be any desired engine parameter. Forexample, the prescribed operating condition may be a weight on wheelscondition indicating the end of an engine cycle. Also, the prescribedoperating condition may be an engine speed condition, time condition, orother engine parameter condition.

Referring now to FIG. 5 , a schematic drawing of a fuel oxygen reductionsystem 500 for a gas turbine engine in accordance with another exemplaryembodiment of the present disclosure is provided. In at least certainexemplary embodiments, the exemplary fuel oxygen reduction system 500depicted may be incorporated into, e.g., the exemplary engine 100described above with reference to FIG. 1 (e.g., may be the fuel oxygenreduction unit 144 depicted in FIG. 1 and described above).

The embodiment illustrated in FIG. 5 includes similar components to theembodiment illustrated in FIG. 4 . For the sake of brevity, thesesimilar components will not all be discussed in conjunction with theembodiment illustrated in FIG. 5 .

Referring to FIG. 5 , the fuel oxygen reduction system 500 for a gasturbine engine includes a fuel tank 502, a fuel oxygen reduction system400 as shown in FIG. 4 , a boost pump 504, a set of valves 510, and aset of pumps 520. The fuel oxygen reduction system 500 can be utilizedwith the fuel oxygen reduction system 400 shown in FIG. 4 and provides aset of valves 510, a set of pumps 520, and a fuel system 500 that coulduse its own pressure to drain out its oxygen rich fuel and then pump ina flow of deoxygenated fuel 427 (FIG. 4 ) to replenish the fuel system.In other words, a system 500 that could quickly and efficiently switchout oxygen rich fuel for a flow of deoxygenated fuel 427 (FIG. 4 ) in afuel system 500.

In embodiments of the present disclosure, the fuel oxygen reductionsystem 400 can be positioned before or after the boost pump 504.

Referring now to FIG. 6 , a flow diagram of a method 300 of operating afuel system for an aeronautical gas turbine engine is provided. Themethod 300 may be utilized with one or more of the exemplary fuelsystems, gas turbine engines, etc. described above, or alternatively maybe utilized with any other suitable fuel system.

The method 300 includes operating the aeronautical gas turbine engineduring a cruise condition. More specifically, the method 300 includes at(301) providing a flow of fuel to a fuel nozzle of the aeronautical gasturbine engine during a cruise condition of the aeronautical gas turbineengine. The method 300 further includes operating the aeronautical gasturbine engine in a wind down condition. More specifically, the method300 includes at (302) providing a flow of fuel to the fuel nozzle of theaeronautical gas turbine engine during a wind down condition. The winddown condition, as noted above, may be an engine operating condition orsequence of operating conditions occurring as the engine transitions tobeing in a completely turned-off condition (i.e., when fuel is no longerprovided to fuel nozzle(s), and the shaft(s) of the engine are notrotating, or are rotating at a low speed). The wind down condition mayinclude a ground idling condition of the engine as the engine is taxiingto its gate at the end of a flight mission (e.g., for commercialaircraft) or hanger, and/or a shutdown sequence of the engine in whichit transitions from the ground idling condition to the completely turnedoff condition. In such a manner, it will be appreciated that providingthe flow of fuel to the fuel nozzle at (302) includes at (304) providingfuel to the fuel nozzle at a first flowrate to facilitate the engineoperating at the desire operating speed (e.g., idle).

The exemplary method 300 further includes at (306) operating a fueloxygen reduction unit to reduce an oxygen content of the flow of fuelprovided to the fuel nozzle of the aeronautical gas turbine engineduring the wind down condition. The fuel oxygen reduction unit may beconfigured in a similar manner as one or more of the exemplary secondaryfuel oxygen reduction units described above with reference to FIGS. 1through 5 , or alternatively may be any other suitable fuel oxygenreduction unit.

In such a manner, it will be appreciated that in at least certainexemplary aspects, operating the fuel oxygen reduction unit at (306)includes at (308) operating the fuel oxygen reduction unit substantiallyexclusively during the wind down condition. In the context of this step,“substantially exclusively” refers to at least 90% of a total operatingtime within a particular flight mission of an aircraft incorporating thefuel oxygen reduction unit.

In such a manner, it will be appreciated that the fuel oxygen reductionunit may define a maximum operating time of one hour or less per flightmission, such as 30 minutes or less per flight mission.

Additionally, or alternatively, it will be appreciated that an aircraftincorporating the aeronautical gas turbine engine may define a maximumfuel capacity (e.g., a maximum amount of fuel that may be loaded in thefuel tanks of the aircraft during typical operations). The fuel oxygenreduction unit may define a maximum volume of fuel throughput per flightmission, with the maximum volume of fuel throughput of the fuel oxygenreduction unit being less than 10 percent of the maximum fuel capacityof the aircraft.

Additionally, or alternatively, still, the fuel oxygen reduction unitmay define a maximum fuel flowrate capacity. The maximum fuel flowratecapacity of the fuel oxygen reduction unit may refer to a maximumflowrate that the fuel oxygen reduction unit may effectively process(i.e., may process at an oxygen reduction level of at least 50% of itsmaximum oxygen reduction level). Further, as noted above, the method 300includes operating the aeronautical gas turbine engine during a cruisecondition. Operating the aeronautical gas turbine engine during thecruise condition may include providing a fuel flow to a combustionsection of the aeronautical gas turbine engine at a cruise conditionflowrate. The maximum fuel flowrate capacity of the fuel oxygenreduction unit is less than the cruise condition flowrate. In such amanner, it will be appreciated that the fuel oxygen reduction unit isnot a steady state fuel oxygen reduction unit, and instead is a specialpurpose fuel oxygen reduction unit.

In such a manner, it will be appreciated that in other exemplaryaspects, the fuel oxygen reduction unit is configured to operatesubstantially continuously. In such a configuration, the fuel oxygenreduction unit may still define the maximum fuel flowrate capacity. Themaximum fuel flowrate capacity may still be less than the cruisecondition flowrate, and the fuel provided to the gas turbine engine maysimply not be effectively conditioned. Notably, however, it will beappreciated that depending on the operating temperatures of the gasturbine engine, the fuel flowrate, the resonance time of the fuel withina combustion section of the gas turbine engine, etc., the fuel may notneed to be effectively conditioned by the fuel oxygen reduction unitduring, e.g., cruise operations. The fuel oxygen reduction unit maystill effectively treat substantially all of the fuel flow to the gasturbine engine during a wind down condition.

Referring still to the exemplary aspect of FIG. 6 , the method 300further includes at (310) ceasing providing the flow of fuel to the fuelnozzle of the aeronautical gas turbine engine, the fuel nozzlecomprising a volume of fuel after ceasing providing the flow of fuel tothe fuel nozzle. In such a manner, it will be appreciated that in theexemplary aspect shown, ceasing providing the flow of fuel to the fuelnozzle of the aeronautical gas turbine engine at (310) includes at (312)maintaining the volume of fuel in the fuel nozzle after the wind downcondition. Notably, the volume of fuel remaining in the fuel nozzle maybe at least about 10 milliliters, and ceasing providing the flow of fuelto the fuel nozzle of the aeronautical gas turbine engine at (310) mayimmediately follow the wind down condition of the engine. In exemplaryembodiments, the volume of fuel may be at least 10 milliliters of fuel,such as at least 20 milliliters of fuel, such as at least 50 millilitersof fuel, such as at least 100 milliliters of fuel and up to three (3)liters of fuel.

The exemplary method 300 may facilitate preventing a fuel within thefuel nozzles from coking or otherwise deteriorating beyond a thresholdamount after the wind down condition of the engine, despite apotentially relatively high temperature that may be reached by the fuelas a result of heat soak-back. For example, in the exemplary aspectdepicted, it will be appreciated that operating the fuel oxygenreduction unit at (306) includes at (314) operating the fuel oxygenreduction unit to reduce an oxygen content of the volume of fuel in thefuel nozzle to less than 20 parts per million, and more specificallyincludes at (316) operating the fuel oxygen reduction unit to reduce theoxygen content of the volume of fuel in the fuel nozzle to less than 15parts per million.

Notably, the method 300 further includes at (315) operating theaeronautical gas turbine engine during an idle condition. The gasturbine engine defines a turbine inlet temperature greater than 1000degrees Fahrenheit while the aeronautical gas turbine engine isoperating during the idle condition at (315). In certain exemplaryembodiments, the turbine inlet temperature, T3, which may be indicativeof an overall temperature of the core, may be at least 1000 degreesFahrenheit during idle standard day conditions (e.g., sea level and 70degrees Fahrenheit ambient), such as at least 1100 degrees Fahrenheit,such as at least 1250 degrees Fahrenheit, such as at least 1400 degreesFahrenheit, such as at least 1500 degrees Fahrenheit, such as at least1550 degrees Fahrenheit, and up to 3500 degrees Fahrenheit.

Further, it will be appreciated that from the discussions above withrespect to FIGS. 1 through 6 , the core of the engine may define arelatively high thermal mass. In such a manner, it will be appreciatedthat the combination of the relatively high turbine inlet temperaturesduring idle and the relatively high thermal mass, the soak-back may berelatively significant, such that the reduction in oxygen content of thevolume of fuel remaining in the fuel nozzle is necessary to reduce arisk of the fuel coking beyond a certain threshold.

Such may allow the volume of fuel remaining in the fuel nozzles towithstand the relatively high temperatures without coking beyond athreshold level.

It will further be appreciated that in certain exemplary aspects, anoxygen level of a fuel flow to the fuel nozzle may be monitored and/orreduced during other operating conditions of the engine. For example,referring now to FIG. 7 , a flow diagram of a method 300 for operating afuel system for an aeronautical gas turbine engine in accordance withanother exemplary aspect of the present disclosure is provided. Themethod 300 may be utilized with one or more of the exemplary fuelsystems, gas turbine engines, etc. described above, or alternatively maybe utilized with any other suitable fuel system.

The method 300 of FIG. 7 is similar to the method 300 of FIG. 6 . Forexample, the method 300 of FIG. 7 generally includes at (302) providinga flow of fuel to a fuel nozzle of the aeronautical gas turbine engineduring a wind down condition; at (306) operating a fuel oxygen reductionunit to reduce an oxygen content of the flow of fuel provided to thefuel nozzle of the aeronautical gas turbine engine during the wind downcondition; and at (310) ceasing providing the flow of fuel to the fuelnozzle of the aeronautical gas turbine engine.

However, for the exemplary aspect of FIG. 7 , an oxygen level of a fuelflow to the fuel nozzle may be further monitored and/or reduced duringother operating conditions of the engine.

For example, for the exemplary aspect of FIG. 7 , the method 300includes at (320) providing a flow of fuel to the fuel nozzle of theaeronautical gas turbine engine during a second condition separate fromthe wind down condition. For the exemplary aspect depicted, an oxygencontent of the flow of fuel to the fuel nozzle of the aeronautical gasturbine engine during the second condition is greater than the oxygencontent of the volume of fuel in the fuel nozzle after ceasing providingthe flow of fuel to the fuel nozzle. For example, in certain exemplaryaspects, the oxygen content of the flow of fuel to the fuel nozzle ofthe aeronautical gas turbine engine during the flight condition is atleast 1.5 times greater than the oxygen content of the volume of fuel inthe fuel nozzle after ceasing providing the flow of fuel to the fuelnozzle.

More specifically, for the embodiment shown, providing the flow of fuelto the fuel nozzle during the second condition at (320) includes at(322) providing a second flow of fuel to the fuel nozzle of theaeronautical gas turbine engine. An oxygen content of the volume of fuelin the fuel nozzle after ceasing providing the flow of fuel to the fuelnozzle at (310) is a first value, and the oxygen content of the secondflow of fuel provided to the fuel nozzle during the second condition at(322) is a second value. The second value is equal to at least 1.5 timesthe first value. More specifically, in at least certain exemplaryaspects the second value is equal to at least three times the firstvalue, such as at least five times the first value, such as up to 100times the first value.

In certain exemplary aspects, the second condition is a flight conditionof the engine. For example, in certain exemplary aspects, the secondcondition is a takeoff flight condition, a climb flight condition, orboth.

Referring still to the exemplary aspect of FIG. 7 , the method furtherincludes at (324) providing a flow of fuel to the fuel nozzle of theaeronautical gas turbine engine during a third condition separate fromthe wind down condition and the second condition. Providing the flow offuel to the fuel nozzle during the third condition at (324) includes at(326) providing a third flow of fuel to the fuel nozzle of theaeronautical gas turbine engine during the third. Similar to theexemplary aspects above, the oxygen content of the third flow of fuelprovided to the fuel nozzle during the third condition is a third value.The third value is less than the second value and greater than the firstvalue. With such an exemplary aspect, it will be appreciated that thesecond condition is a relatively high power flight condition, and thethird condition is a relatively low power flight condition. For example,the second condition may be a takeoff flight condition, a climb flightcondition, or both, and the third condition may be a cruise flightcondition.

In certain exemplary aspects, a primary fuel oxygen reduction unit maybe operated during the second and third conditions (and optionallyduring the first condition) (see FIG. 1 ).

In such a manner, it will be appreciated that a fuel flow to the fuelnozzles is higher during the second and third conditions, than duringthe wind down condition. In such a manner the fuel is not exposed to thehigh temperatures for as long, and the volume of fuel thorough the fuelnozzle is greater, such that there is less risk of fuel coking withinthe nozzle.

In an exemplary aspect of the present disclosure, a method is providedfor operating a fuel delivery system for a gas turbine engine. Themethod includes receiving an inlet fuel flow in a fuel oxygen reductionunit for reducing an amount of oxygen in the inlet fuel flow using astripping gas flow through a stripping gas flowpath; and passing thestripping gas flow through the fuel oxygen reduction unit a single time.

Further aspects of the invention are provided by the subject matter ofthe following clauses:

1. A fuel oxygen reduction unit for an engine comprising: an inlet fuelline; a stripping gas source; a contactor selectively in fluidcommunication with the stripping gas source, the inlet fuel line, orboth to form a fuel/gas mixture; and a separator that receives thefuel/gas mixture, the separator configured to separate the fuel/gasmixture into an outlet stripping gas flow and an outlet fuel flow;wherein a flow of stripping gas passes through the fuel oxygen reductionunit a single time.

2. The fuel oxygen reduction unit of any preceding clause, furthercomprising a valve downstream of the stripping gas source and upstreamof the contactor, wherein the valve is transitionable between a closedposition in which the stripping gas source is not in fluid communicationwith the contactor, and an open position in which the stripping gasflows to the contactor.

3. The fuel oxygen reduction unit of any preceding clause, wherein thevalve transitions to the open position at a prescribed operatingcondition.

4. The fuel oxygen reduction unit of any preceding clause, wherein theprescribed operating condition is a weight on wheels condition.

5. The fuel oxygen reduction unit of any preceding clause, wherein theprescribed operating condition is an engine speed condition.

6. The fuel oxygen reduction unit of any preceding clause, wherein theprescribed operating condition is a wind down condition of the engine.

7. The fuel oxygen reduction unit of any preceding clause, wherein thefuel oxygen reduction unit defines a maximum continuous operating timeof one hour or less.

8. The fuel oxygen reduction unit of any preceding clause, wherein theseparator includes an inlet in fluid communication with the contactorthat receives the fuel/gas mixture, a fuel outlet, and a stripping gasoutlet, wherein the separator is configured to separate the fuel/gasmixture into an outlet stripping gas flow and an outlet fuel flow andprovide the outlet stripping gas flow to the stripping gas outlet andthe outlet fuel flow to the fuel outlet.

9. The fuel oxygen reduction unit of any preceding clause, wherein theoutlet stripping gas flow is vented out to atmosphere downstream of theseparator.

10. The fuel oxygen reduction unit of any preceding clause, wherein thestripping gas source comprises a rechargeable bottle of inert gas.

11. The fuel oxygen reduction unit of any preceding clause, wherein thestripping gas source comprises an inert gas generator.

12. The fuel oxygen reduction unit of any preceding clause, wherein theoutlet fuel flow has a lower oxygen content than the inlet fuel flow,and wherein the outlet stripping gas flow has a higher oxygen contentthan the inlet stripping gas flow.

13. A fuel oxygen reduction system for an engine comprising: an inletfuel line; a stripping gas source; a contactor selectively in fluidcommunication with the stripping gas source, the inlet fuel line, orboth to form a fuel/gas mixture; a separator that receives the fuel/gasmixture, the separator configured to separate the fuel/gas mixture intoan outlet stripping gas flow and an outlet fuel flow; and a storage tankthat receives the outlet fuel flow.

14. The fuel oxygen reduction system of any preceding clause, whereinthe stripping gas source comprises an inert gas generator.

15. The fuel oxygen reduction system of any preceding clause, furthercomprising a primary tank containing a primary fuel flow; and a valvedownstream of the storage tank and the primary tank, wherein the valveis transitionable between a first position in which the primary tank isin fluid communication with the engine, and a second position in whichthe storage tank is in fluid communication with the engine.

16. The fuel oxygen reduction system of any preceding clause, whereinthe second valve transitions to the second position at a prescribedoperating condition.

17. The fuel oxygen reduction system of any preceding clause, whereinthe prescribed operating condition is a weight on wheels condition.

18. The fuel oxygen reduction system of any preceding clause, whereinthe prescribed operating condition is an engine speed condition.

19. The fuel oxygen reduction system of any preceding clause, whereinthe primary tank defines a first volume, wherein the storage tankdefines a second volume, and wherein the second volume is less than 20%of the first volume.

20. The fuel oxygen reduction system of any preceding clause, whereinthe separator includes an inlet in fluid communication with thecontactor that receives the fuel/gas mixture, a fuel outlet, and astripping gas outlet, wherein the separator is configured to provide theoutlet stripping gas flow to the stripping gas outlet and the outletfuel flow to the storage tank via the fuel outlet.

21. A method of operating a fuel system for an aeronautical gas turbineengine, the method comprising: providing a flow of fuel to a fuel nozzleof the aeronautical gas turbine engine during a wind down condition;operating a fuel oxygen reduction unit to reduce an oxygen content ofthe flow of fuel provided to the fuel nozzle of the aeronautical gasturbine engine during the wind down condition; and ceasing providing theflow of fuel to the fuel nozzle of the aeronautical gas turbine engine,the fuel nozzle comprising a volume of fuel after ceasing providing theflow of fuel to the fuel nozzle; wherein operating the fuel oxygenreduction unit comprises operating the fuel oxygen reduction unit toreduce an oxygen content of the volume of fuel in the fuel nozzle toless than 20 parts per million.

22. The method of one or more of these clauses, wherein operating thefuel oxygen reduction unit comprises operating the fuel oxygen reductionunit to reduce the oxygen content of the volume of fuel in the fuelnozzle to less than 15 parts per million.

23. The method of one or more of these clauses, further comprising:operating the aeronautical gas turbine engine during an idle condition,wherein the gas turbine engine defines a turbine inlet temperaturegreater than 1000 degrees Fahrenheit while the aeronautical gas turbineengine is operating during the idle condition.

24. The method of one or more of these clauses, wherein the aeronauticalgas turbine engine comprises a core defining a thermal mass.

25. The method of one or more of these clauses, wherein operating thefuel oxygen reduction unit comprises operating the fuel oxygen reductionunit substantially exclusively during the wind down condition.

26. The method of one or more of these clauses, wherein the fuel oxygenreduction unit defines a maximum operating time of one hour or less perflight mission.

27. The method of one or more of these clauses, wherein the aeronauticalgas turbine engine is incorporated into an aircraft, wherein theaircraft defines a maximum fuel capacity, wherein the fuel oxygenreduction unit defines a maximum volume of fuel throughput per flightmission, and wherein the maximum volume of fuel throughput is less than10 percent of the maximum fuel capacity of the aircraft.

28. The method of one or more of these clauses, further comprising:operating the aeronautical gas turbine engine during a cruise condition,wherein operating the aeronautical gas turbine engine during the cruisecondition comprises providing a fuel flow to a combustion section of theaeronautical gas turbine engine at a cruise condition flowrate, whereinthe fuel oxygen reduction unit defines a maximum fuel flowrate capacity,and wherein the maximum fuel flowrate capacity of the fuel oxygenreduction unit is less than the cruise condition flowrate.

29. The method of one or more of these clauses, further comprising:providing a flow of fuel to the fuel nozzle of the aeronautical gasturbine engine during a second condition separate from the wind downcondition, wherein an oxygen content of the flow of fuel to the fuelnozzle of the aeronautical gas turbine engine during the secondcondition is greater than the oxygen content of the volume of fuel inthe fuel nozzle after ceasing providing the flow of fuel to the fuelnozzle.

30. The method of one or more of these clauses, wherein the oxygencontent of the flow of fuel to the fuel nozzle of the aeronautical gasturbine engine during the flight condition is at least 1.5 times greaterthan the oxygen content of the volume of fuel in the fuel nozzle afterceasing providing the flow of fuel to the fuel nozzle.

31. The method of one or more of these clauses, further comprising:providing a second flow of fuel to the fuel nozzle of the aeronauticalgas turbine engine during a second condition separate from the wind downcondition, wherein an oxygen content of the volume of fuel in the fuelnozzle after ceasing providing the flow of fuel to the fuel nozzle is afirst value, wherein the oxygen content of the second flow of fuelprovided to the fuel nozzle during the second condition is a secondvalue, and wherein the second value is equal to at least 1.5 times thefirst value.

32. The method of one or more of these clauses, wherein the second valueis equal to at least 3 times the first value.

33. The method of one or more of these clauses, wherein the secondcondition is a flight condition.

34. The method of one or more of these clauses, wherein the secondcondition is a takeoff flight condition, a climb flight condition, orboth.

35. The method of one or more of these clauses, further comprising:providing a third flow of fuel to the fuel nozzle of the aeronauticalgas turbine engine during a third condition separate from the wind downcondition, wherein the oxygen content of the third flow of fuel providedto the fuel nozzle during the third condition is a third value, whereinthe third value is less than the first value, wherein the secondcondition is a relatively high power flight condition, and wherein thethird condition is a relatively low power flight condition.

36. The method of one or more of these clauses, wherein the volume offuel in the fuel nozzle is at least 10 milliliters of fuel.

37. The method of one or more of these clauses, wherein ceasingproviding the flow of fuel to the fuel nozzle of the aeronautical gasturbine engine comprises maintaining the volume of fuel in the fuelnozzle during and after the wind down condition.

38. A method is provided for operating a fuel delivery system for a gasturbine engine. The method includes receiving an inlet fuel flow in afuel oxygen reduction unit for reducing an amount of oxygen in the inletfuel flow using a stripping gas flow through a stripping gas flowpath;and passing the stripping gas flow through the fuel oxygen reductionunit a single time.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they include structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

While this disclosure has been described as having exemplary designs,the present disclosure can be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the disclosure using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this disclosure pertains and which fallwithin the limits of the appended claims.

What is claimed is:
 1. A fuel oxygen reduction unit for an enginecomprising: an inlet fuel line; a stripping gas source; a contactorselectively in fluid communication with the stripping gas source and theinlet fuel line to form a fuel/gas mixture; a separator that receivesthe fuel/gas mixture, the separator configured to separate the fuel/gasmixture into an outlet stripping gas flow and an outlet fuel flow;wherein a flow of stripping gas passes through the fuel oxygen reductionunit a single time, the flow of stripping gas is not recirculated backto the fuel oxygen reduction unit, the flow of stripping gas is notrecirculated back to the contactor, and the outlet stripping gas flowdoes not flow through a gas oxygen reduction portion; and a valvedownstream of the stripping gas source and upstream of the contactor,wherein the valve is transitionable between a closed position in whichthe stripping gas source is not in fluid communication with thecontactor, and an open position in which the stripping gas flows to thecontactor, and wherein the valve transitions to the open position at aprescribed operating condition that indicates the engine is at an end ofan operating cycle.
 2. The fuel oxygen reduction unit of claim 1,wherein the prescribed operating condition is a weight on wheelscondition.
 3. The fuel oxygen reduction unit of claim 1, wherein theprescribed operating condition is an engine speed condition.
 4. The fueloxygen reduction unit of claim 1, wherein the prescribed operatingcondition is a wind down condition of the engine.
 5. The fuel oxygenreduction unit of claim 1, wherein the fuel oxygen reduction unitdefines a maximum continuous operating time of one hour or less.
 6. Thefuel oxygen reduction unit of claim 1, wherein the engine defines adesired fuel flow when operated in a cruise condition, and wherein theoutlet fuel flow is less than the desired fuel flow.
 7. The fuel oxygenreduction unit of claim 1, wherein the separator includes an inlet influid communication with the contactor that receives the fuel/gasmixture, a fuel outlet, and a stripping gas outlet, wherein theseparator is configured to separate the fuel/gas mixture into an outletstripping gas flow and an outlet fuel flow and provide the outletstripping gas flow to the stripping gas outlet and the outlet fuel flowto the fuel outlet, and wherein the outlet stripping gas flow is ventedout to atmosphere downstream of the separator.
 8. The fuel oxygenreduction unit of claim 1, wherein the stripping gas source comprises arechargeable bottle of inert gas.
 9. The fuel oxygen reduction unit ofclaim 1, wherein the stripping gas source comprises an inert gasgenerator.
 10. The fuel oxygen reduction unit of claim 1, wherein theoutlet fuel flow has a lower oxygen content than the inlet fuel flow,and wherein the outlet stripping gas flow has a higher oxygen contentthan the inlet stripping gas flow.
 11. A fuel oxygen reduction systemfor an engine comprising: an inlet fuel line; a stripping gas source; acontactor selectively in fluid communication with the stripping gassource and the inlet fuel line to form a fuel/gas mixture; a separatorthat receives the fuel/gas mixture, the separator configured to separatethe fuel/gas mixture into an outlet stripping gas flow and an outletfuel flow; a storage tank that receives the outlet fuel flow; a primarytank containing a primary fuel flow; and a valve downstream of thestorage tank and the primary tank, wherein the valve is transitionablebetween a first position in which the primary tank is in fluidcommunication with the engine, and a second position in which thestorage tank is in fluid communication with the engine.
 12. The fueloxygen reduction system of claim 11, wherein the primary tank defines afirst volume, wherein the storage tank defines a second volume, andwherein the second volume is less than 20% of the first volume.
 13. Thefuel oxygen reduction system of claim 11, wherein the valve transitionsto the second position at a prescribed operating condition.
 14. The fueloxygen reduction system of claim 11, wherein the prescribed operatingcondition is a weight on wheels condition.
 15. The fuel oxygen reductionsystem of claim 11, wherein the prescribed operating condition is anengine speed condition.
 16. The fuel oxygen reduction system of claim11, wherein the stripping gas source comprises an inert gas generator.17. The fuel oxygen reduction system of claim 11, wherein the separatorincludes an inlet in fluid communication with the contactor thatreceives the fuel/gas mixture, a fuel outlet, and a stripping gasoutlet, wherein the separator is configured to provide the outletstripping gas flow to the stripping gas outlet and the outlet fuel flowto the storage tank via the fuel outlet.